"The otherworld has seven realms," said Stella as she walked the new American girl named Bloom on a tour around The Magic School of Alfea Campus. It's a Hogwarts kind-of-school for fairies they even make reference to Harry Poter in episode 1. Unlike a great deal of the studentship at Alfea, Bloom is the odd-girl out, she was born as a human but from a "dormant bloodline." Bloom is a Changeling.
What's a Changeling? According to Wikipedia:
A changeling, also historically referred to as an auf or oaf, is a human-like creature found in folklore and folk religion throughout Europe. A changeling was believed to be a fairy child that had been left in place of a human child stolen by the fairies.
FATE unknown is encapsulated into this series tale? A bigger question is, why are fairies baby-swapping with unsuspecting humans? How long has this been going on and what's the end game?